Presently, when a nurseryman wants to sell his tree or shrub, he must dig the plant out of the ground with the root system of the plant as intact as possible. Next he must protect the root system. Some deciduous trees or shrubs can be dug up during the dormant season barerooted, moved with minimum protection, and transplanted successfully.
However, evergreen trees and shrubs and deciduous trees and shrubs in the growing season must be moved with some amount of soil attached to the plants in which the root systems are kept intact. The success of transplanting trees and shrubs depends on the existence of healthy root systems.
In order to move a tree or shrub, the ball-and-burlap method, the container growing method, and tree moving machine methods are commercially available.
According to the ball-and-burlap method, a trench must be dug around a tree. The circumference and depth of the trench depend on the size and kind of the tree. Then, the soil ball within the trench must be separated from the ground at its base. The ball of earth is held in place by wrapping it with burlap securely tied with rope. This method is time consuming and expensive because it can only be done by experienced workers. The ball-and-burlap method is not always successful. When root system of a plant spreads thinly into the ground, the ball-and-burlap method removes the plant out of the ground with only a few short-cut thick roots which eventually can not support or feed the entire plant. Thus, a few years prior to the ball-and-burlap operation, tree roots are often pruned by digging trench around the tree, in such a manner that digging is done for one third of the trench in the first year, next one third in the second year, and finally the last one third in the third year. This root pruning encourages dense root formation inside the trench inner boundry. The balled-and-burlapped plants prepared after root pruning have almost 100% success in transplanting.
The soil ball is easily broken and this would result in root damage. Thus, the ball-and-burlap method can not be mechanized. There are many other shortcomings to this method. The soil ball is heavy to handle, easily broken, and difficult to maintain at the garden center because burlap often decomposes at inopportune times.
The so-called container-grown trees and shrubs are easy to handle at nurseries and garden centers. To grow trees and shrubs in containers, small plants are planted in metal or plastic containers with special media. Several disadvantages accrue from this method. Intensive care must be given to the plants until plants attain salable size. This may be for 1-2 years or longer. Since container-grown plants have no contact with the ground which would otherwise provide water and nutrients to field-grown plants, these trees and shrubs must be fed at least 1-2 times daily with water and nutrients. Secondly, pest problems are prevalent among these because plant density is high. Thirdly, plants are kept in a high moisture environment due to frequent watering. This also makes plants more vulnerable to disease. The greatest difficulty in the method is overwintering during the winter season, particularly in mid to northern United States. Plant roots are very sensitive to low temperature - even 32.degree. F is fatal in many cases. The root system of field-grown plants are protected by mother earth. But container-grown plants must be kept in greenhouses or plastic houses often employing heating devices during the winter season. The energy crisis makes this situation undesirable. Plants in containers also suffer from Summer heat. Temperature of containers often rises so high that it causes the reduction of growth in root and stem.
Several kinds of tree movers, which dig and carry trees to pre-dug holes, have been commercially available. The U.S. Pat. No. 3,284,932 (E. A. Wendlandt) describes a device to dig a tree with a cylindrical soil ball. Tree movers or such a tree digger are only good for the moving of trees for a short distance.
In addition, the U.S. Pat. No. 3,662,490 (R. S. Childs) describes a method to dig a tree with a cylindrical soil ball and place a cylindrical sleeve around the ball. A disc is then fastened to the base of the sleeve to make a bottom.
The U.S. Pat. No. 3,154,884 (S. S. Amar et al.), U.S. Pat. No. 1,634,727 (W. O. Roy), and U.S. Pat. No. 3,828,473 (D. H. Morey) describe methods to grow plants in bottom-less containers. Vegetable seeds are planted in containers which have been inserted in the soil (Amar et al.), plants are planted in tubes with soil and then the tubes are inserted in the soil (Roy), or a plant is planted in a tube with special medium; the plant is pushed out of the tube into a pre-dug hole in the ground after the plant reaches the certain size (Morey).
In short, nothing has described a method to grow trees and shrubs in hollow cylinders which are inserted into the ground around the root system after trees and shrubs reach nearly salable size. There has been no simple method to pot a plant in which root system is enclosed in a hollow cylinder.